Plunger tip, injection device, and injection method

ABSTRACT

A plunger tip includes a main body of the plunger tip. A first cooling chamber is provided at a central region of a tip end of the main body of the plunger tip inside the main body of the plunger tip. A second cooling chamber is provided along an outer peripheral surface of the tip end inside the main body of the plunger tip. The second cooling chamber is configured such that a cooling medium is caused to flow in the second cooling chamber in priority to the first cooling chamber.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2020-003651 filed on Jan. 14, 2020, incorporated herein by reference inits entirety.

BACKGROUND 1. Technical Field

The disclosure relates to a plunger tip, an injection device, and aninjection method.

2. Description of Related Art

A die casting apparatus is equipped with an injection device thatinjects a molten metal to fill in a metal mold with the molten metal.The injection device includes a cylindrical plunger sleeve, a plungertip that is slidably installed in the plunger sleeve, and a plunger rodthat causes the plunger tip to slide.

Here, in order to improve injection performance, it is required for theinjection device to minimize friction between the plunger tip and theplunger sleeve so as to allow the plunger tip to slide smoothly.

A technique related to the injection device is disclosed in, forexample, Japanese Unexamined Patent Application Publication No.2016-68106 (JP 2016-68106 A). The injection device disclosed in JP2016-68106 A promotes cooling of the molten metal after the molten metalis injected into the metal mold by causing coolant to flow inside theplunger tip. Further, in the injection device above, the coolant is usedto sufficiently cool an outer peripheral surface near a tip end surfaceof the plunger tip to suppress occurrence of friction caused by contactbetween the outer peripheral surface near the tip end surface of theplunger tip and an inner peripheral surface of the plunger sleeve.

SUMMARY

In the injection device disclosed in JP 2016-68106 A, cooling of themolten metal needs to be started using the coolant in the plunger tip ata relatively late timing such that the molten metal stored in the in theinjection device is not solidified before being injected into the metalmold. However, by the time when cooling of the molten metal is startedat such a timing, the molten metal has already entered a gap between theouter peripheral surface of the tip end of the plunger tip and theplunger sleeve. Therefore, burrs are created in the gap between theouter peripheral surface of the tip end of the plunger tip and theplunger sleeve as the molten metal that has entered the gap issolidified. Thus, in the injection device, friction between the plungertip and plunger sleeve is increased as being influenced by the burrs,which disables smooth sliding of the plunger tip. Therefore, there maybe a case where injection performance deteriorates.

The disclosure provides a plunger tip, an injection device, and aninjection method capable of improving injection performance bysuppressing creation of burrs.

A first aspect of the disclosure relates to a plunger tip. The plungertip includes a main body of the plunger tip. In the plunger tip, a firstcooling chamber is provided at a central region of a tip end of the mainbody of the plunger tip inside the main body of the plunger tip, and asecond cooling chamber is provided inside the main body of the plungertip along an outer peripheral surface of the tip end. The second coolingchamber is configured such that a cooling medium flows in the secondcooling chamber in priority to the first cooling chamber.

According to the first aspect, the molten metal in proximity to theentrance of the gap between the outer peripheral surface of the tip endof the plunger tip and the plunger sleeve can be solidified using thesecond cooling chamber before the molten metal enters the gap.Therefore, creation of burrs between the plunger tip and the plungersleeve can be suppressed. With this configuration, friction between theplunger tip and the plunger sleeve is reduced, which enables smoothsliding of the plunger tip. Accordingly, injection performance isimproved.

In the first aspect, the second cooling chamber may be configured suchthat the cooling medium flows at a timing earlier than a timing of thefirst cooling chamber.

In the aspect above, the second cooling chamber may be configuredindependently of the first cooling chamber and configured such that thecooling medium different from a cooling medium flowing in the firstcooling chamber flows in the second cooling chamber.

With the configuration above, the molten metal in proximity to theentrance of the gap between the outer peripheral surface of the tip endof the plunger tip and the plunger sleeve can be solidified using thesecond cooling chamber before the molten metal enters the gap.Therefore, creation of burrs between the plunger tip and the plungersleeve can be suppressed. With this configuration, friction between theplunger tip and the plunger sleeve is reduced, which enables smoothsliding of the plunger tip. Accordingly, injection performance isimproved.

In the aspect above, the cooling medium to flow in the second coolingchamber of the plunger tip may be liquid nitrogen. With theconfiguration above, the molten metal in proximity to the entrance ofthe gap can be solidified more quickly than when coolant is used.

In the aspect above, the outer peripheral surface of the tip end of theplunger tip may include a stepped shape. With this configuration, themolten metal can be solidified quickly at a stepped portion in proximityto the entrance of the gap between the outer peripheral surface of thetip end of the plunger tip and the plunger sleeve before the moltenmetal enters and reaches the depth of the gap.

A second aspect of the disclosure relates to an injection device. Theinjection device includes a plunger sleeve having a cylindrical shape;the plunger tip according to the aspect above, the plunger tip beingconfigured so as to be slidable in a cylinder of the plunger sleeve; anda plunger rod that causes the plunger tip to slide in the cylinder ofthe plunger sleeve.

According to the second aspect, the molten metal in proximity to theentrance of the gap between the outer peripheral surface of the tip endof the plunger tip and the plunger sleeve can be solidified using thesecond cooling chamber before the molten metal enters the gap.Therefore, creation of burrs between the plunger tip and the plungersleeve can be suppressed. With this configuration, friction between theplunger tip and the plunger sleeve is reduced, which enables smoothsliding of the plunger tip. Accordingly, injection performance isimproved.

According to the second aspect, the plunger tip may be configured so asto be rotatable about an axial direction as a rotation axis. With theconfiguration above, a high temperature portion of the plunger tip thatis immersed in the molten metal is switched with a low temperatureportion that is not immersed in the molten metal. Therefore, the moltenmetal in proximity to the entrance of the gap between the outerperipheral surface of the tip end of the plunger tip and the plungersleeve can be solidified more quickly using the low temperature portion.

A third aspect of the disclosure relates to an injection method of aninjection device. The injection device includes a plunger sleeve havinga cylindrical shape, a plunger tip configured to be slidable in acylinder of the plunger sleeve and including a main body of the plungertip, and a plunger rod causing the plunger tip to slide in the cylinderof the plunger sleeve. A first cooling chamber is provided in a centralregion of a tip end of the main body of the plunger tip. A secondcooling chamber is provided along an outer peripheral surface of the tipend inside the main body of the plunger tip. The injection methodincludes: causing a cooling medium to flow in the second cooling chamberin priority to the first cooling chamber; supplying molten metal intothe cylinder of the plunger sleeve; and injecting the molten metal bycausing the plunger tip to slide using the plunger rod while the coolingmedium is caused to flow in the first cooling chamber.

According to the third aspect, the molten metal in proximity to theentrance of the gap between the outer peripheral surface of the tip endof the plunger tip and the plunger sleeve can be solidified using thesecond cooling chamber before the molten metal enters the gap.Therefore, creation of burrs between the plunger tip and the plungersleeve can be suppressed. With this configuration, friction between theplunger tip and the plunger sleeve is reduced, which enables smoothsliding of the plunger tip. Accordingly, injection performance isimproved.

According to the third aspect, the cooling medium may be caused to flowin the second cooling chamber before the molten metal is supplied intothe cylinder of the plunger sleeve.

According to the aspects of the disclosure, the disclosure can providethe plunger tip, the injection device, and the injection method capableof improving injection performance by suppressing creation of burrs.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the disclosure will be described below withreference to the accompanying drawings, in which like signs denote likeelements, and wherein:

FIG. 1 is a schematic sectional view showing a part of an injectiondevice according to a first embodiment;

FIG. 2 is a schematic sectional view of a part of the injection deviceshown in FIG. 1 as seen from the front;

FIG. 3 is a diagram for explaining an operation of the injection deviceaccording to the first embodiment;

FIG. 4 is a diagram for explaining the operation of the injection deviceaccording to the first embodiment;

FIG. 5 is a diagram for explaining the operation of the injection deviceaccording to the first embodiment;

FIG. 6 is a diagram for explaining the operation of the injection deviceaccording to the first embodiment;

FIG. 7 is a diagram for explaining the operation of the injection deviceaccording to the first embodiment;

FIG. 8 is a schematic sectional view showing a part of an injectiondevice according to a second embodiment; and

FIG. 9 is a schematic sectional view showing a part of an injectiondevice according to a third embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, specific embodiments to which the disclosure is appliedwill be described in detail with reference to the drawings. However, thedisclosure is not limited to the following embodiments. Further, thefollowing description and drawings are simplified as appropriate for thesake of clarity.

First Embodiment

FIG. 1 is a schematic sectional view showing a part of an injectiondevice 1 according to a first embodiment. The injection device 1 shownin FIG. 1 is a device that is mounted on a die casting apparatus andinjects a molten metal such as aluminum accumulated in the injectiondevice 1 into a metal mold to fill in the metal mold with the moltenmetal.

Specifically, the injection device 1 includes at least a plunger sleeve11 having a cylindrical shape, a plunger tip 12, and a plunger rod 13.The plunger tip 12 is slidably installed in a cylinder of the plungersleeve 11. The plunger rod 13 causes the plunger tip 12 to slide in thecylinder of the plunger sleeve 11.

The injection device 1 is installed such that the plunger sleeve 11 anda sprue sleeve 71 provided in a metal mold 70 communicate with eachother. In the metal mold 70, a mold sprue 72 is provided in a cylinderof the sprue sleeve 71. The mold sprue 72 is provided at a positionfacing a forward direction of the plunger tip 12 that is slidablyinstalled in the plunger sleeve 11. A runner 73 is provided between thesprue sleeve 71 and the mold sprue 72. Further, a gate 74 (not shown)and a cavity 75 (not shown) are provided at a tip end of the runner 73.

For example, in the injection device 1, when the plunger tip 12 is movedbackward (that is, the plunger tip 12 is slid in a negative direction ofan X-axis), the molten metal is supplied into the cylinder of theplunger sleeve 11 through a molten metal supply port 111 that isprovided in an upper portion of the plunger sleeve 11. As a result, themolten metal is accumulated in a hollow portion 60. The hollow portion60 is a space surrounded by the plunger sleeve 11, the plunger tip 12,and the sprue sleeve 71 and the mold sprue 72 of the metal mold 70.Thereafter, the injection device 1 applies a pressure of an injectioncylinder (not shown) to the plunger tip 12 via the plunger rod 13 tomove the plunger tip 12 forward (that is, to cause the plunger tip 12 toslide in a positive direction of the X-axis). Consequently, the moltenmetal accumulated in the hollow portion 60 is filled in the cavity 75via the sprue sleeve 71, the mold sprue 72, the runner 73, and the gate74 of the metal mold 70.

Subsequently, a cooling mechanism of the injection device 1 will bedescribed with reference to FIG. 2 in addition to FIG. 1. FIG. 2 is aschematic sectional view of the plunger tip 12 provided in the injectiondevice 1 as seen from the front. Note that FIG. 2 is a schematicsectional view of a portion cut along II-IP in FIG. 1.

As shown in FIGS. 1 and 2, a first cooling chamber 121 is providedinside a main body of the plunger tip 12 in the central region of thetip end of the plunger tip 12 (the end on the side facing the mold sprue72). A second cooling chamber 122 is provided inside the main body ofthe plunger tip 12 along an outer peripheral surface of a tip end of theplunger tip 12 (a portion close to the inner peripheral surface of theplunger sleeve 11). The second cooling chamber 122 has an annular shapeso as to surround the first cooling chamber 121 when viewed in a frontview (that is, when viewed from an x-axis direction).

Further, a coolant supply path 121 a is provided in the plunger tip 12from a rear end of the plunger tip 12 (an end on the side of the plungertip 12 connected to the plunger rod 13) to the first cooling chamber121, and a coolant discharge path 121 b extends from the first coolingchamber 121 to the rear end of the plunger tip 12.

Further, the coolant supply path 122 a is provided in the plunger tip 12from the rear end of the plunger tip 12 to the second cooling chamber122, and the coolant discharge path 122 b extends from the secondcooling chamber 122 to the rear end of the plunger tip 12.

In the plunger rod 13, a coolant supply path 131 a, a coolant dischargepath 131 b, a coolant supply path 132 a, and a coolant discharge path132 b are provided to extend from one end (an end connected to theplunger tip 12) to the other end (an end connected to the injectioncylinder (not shown)).

The plunger tip 12 is connected to the one end of the plunger rod 13such that the coolant supply path 121 a and the coolant supply path 131a communicate with each other, the coolant discharge path 121 b and thecoolant discharge path 131 b communicate with each other, the coolantsupply path 122 a and the coolant supply path 132 a communicate witheach other, and the coolant discharge path 122 b and the coolantdischarge path 132 b communicate with each other. An injection cylinder14 (not shown) is connected to the other end of the plunger rod 13, anda coolant supply source 15 and a coolant discharge port 16 (both notshown) are provided at the other end of the plunger rod 13.

A cooling medium M1 such as coolant discharged from the coolant supplysource 15 is supplied to the first cooling chamber 121 via the coolantsupply path 131 a and the coolant supply path 121 a. The cooling mediumM1 supplied to the first cooling chamber 121 is then discharged from thecoolant discharge port 16 via the coolant discharge path 121 b and thecoolant discharge path 131 b.

A cooling medium M2 such as coolant discharged from the coolant supplysource 15 is supplied to the second cooling chamber 122 via the coolantsupply path 132 a and the coolant supply path 122 a. The cooling mediumM2 supplied to the second cooling chamber 122 is then discharged fromthe coolant discharge port 16 via the coolant discharge path 122 b andthe coolant discharge path 132 b.

Here, the second cooling chamber 122 is provided independently of thefirst cooling chamber 121, and the cooling medium M2 different from thecooling medium M1 that flows in the first cooling chamber 121 flows inthe second cooling chamber 122. Therefore, in the injection device 1, atiming of causing the cooling medium M1 to flow in the first coolingchamber 121 and a timing of causing the cooling medium M2 to flow in thesecond cooling chamber 122 can be freely set.

In the injection device 1, the cooling medium M1 flows in the firstcooling chamber 121 so as to cool the molten metal accumulated in thehollow portion 60 to such an extent that the molten metal is notsolidified, thereby cooling of the injected molten metal filled in thecavity of the metal mold 70 can be promoted. Further, after that,detachability between the plunger tip 12 and a biscuit produced bysolidifying the molten metal can be improved.

However, in the injection device 1, cooling of the molten metal usingthe first cooling chamber 121 needs to be started at a relatively latetiming in order to suppress that the molten metal accumulated in thehollow portion 60 is solidified in the hollow portion 60 before beinginjected into the cavity of the metal mold 70.

However, there is a possibility that, by the time when cooling of themolten metal is started at such a timing, the molten metal has alreadyentered a gap between the outer peripheral surface of the tip end of theplunger tip 12 and the plunger sleeve 11. Therefore, there is also apossibility that burrs are created in the gap between the outerperipheral surface of the tip end of the plunger tip 12 and the plungersleeve 11 as the molten metal that has entered the gap is solidified.Thus, friction between the plunger tip 12 and plunger sleeve 11 isincreased as being influenced by the burrs, which disables smoothsliding of the plunger tip 12. Therefore, there may be a case whereinjection performance deteriorates.

Accordingly, in the injection device 1, the cooling medium M2 is causedto flow in the second cooling chamber 122 before causing the coolingmedium M1 to flow in the first cooling chamber 121 such that the moltenmetal in proximity to an entrance of the gap between the outerperipheral surface of the tip end of the plunger tip 12 and the plungersleeve 11 is solidified before the molten metal enters the gap. Withthis configuration, in the injection device 1, creation of burrs betweenthe outer peripheral surface of the tip end of the plunger tip 12 andthe plunger sleeve 11 can be suppressed, which enables smooth sliding ofthe plunger tip 12. Accordingly, the injection performance can beimproved.

Next, operations of the injection device 1 will be described withreference to FIGS. 3 to 7. FIGS. 3 to 7 are diagrams for explaining theoperations of the injection device 1. Note that, FIG. 5 is an enlargedview of an area A in FIG. 4.

First, as shown in FIG. 3, the plunger tip 12 is moved backward. Thatis, the plunger tip 12 is slid in the negative direction of the X-axis.

After that, as shown in FIG. 4, molten metal 50 is supplied into thecylinder of the plunger sleeve 11 from the molten metal supply port 111of the plunger sleeve 11. Consequently, the molten metal 50 isaccumulated in the hollow portion 60 (a space surrounded by the plungersleeve 11, the plunger tip 12, and the sprue sleeve 71 and the moldsprue 72 of the metal mold 70).

At this time, the cooling medium M2 is caused to flow in the secondcooling chamber 122. With this configuration, the molten metal 50 inproximity to the entrance of the gap between the outer peripheralsurface of the tip end of the plunger sleeve 11 and the plunger tip 12can be solidified before the molten metal 50 enters the gap (see FIG.5). With a solidified metal 51 described above, creation of burrsbetween the outer peripheral surface of the tip end of the plunger tip12 and the plunger sleeve 11 can be suppressed in the injection device1.

Note that, the timing of causing the cooling medium M2 to flow in thesecond cooling chamber 122 (that is, the timing of starting cooling ofthe molten metal 50 using the second cooling chamber 122) is preferablyprior to supply of the molten metal 50 into the hollow portion 60.However, the timing of causing the cooling medium M2 to flow may beafter the molten metal 50 is supplied to the hollow portion 60 as longas the timing occurs before the molten metal 50 enters the gap betweenthe plunger sleeve 11 and the plunger tip 12.

After that, as shown in FIG. 6, the plunger tip 12 is moved forward.Accordingly, the volume of the hollow portion 60 is reduced, and thehollow portion 60 is filled with the molten metal 50. Even at this time,the cooling medium M2 is continuously caused to flow in the secondcooling chamber 122. With this configuration, even in a portion of thegap that is to be newly immersed in the molten metal 50 due to rising ofa surface of the molten metal 50 in the hollow portion 60, only themolten metal 50 in proximity to an entrance of the portion of the gapcan be solidified before the molten metal 50 enters the portion of thegap. Consequently, in the injection device 1, creation of burrs (e.g. socalled gap burrs and wedge burrs) that is caused by the molten metalentering the gap between the outer peripheral surface of the tip end ofthe plunger tip 12 and the plunger sleeve 11 and that increases asliding resistance can be suppressed.

After that, as shown in FIG. 7, the plunger tip 12 is moved furtherforward at a high pressure while causing the cooling medium M1 to flowin the first cooling chamber 121. The forward movement of the plungertip 12 shown in FIG. 6 and the further forward movement of the plungertip 12 shown in FIG. 7 may be performed stepwise or continuously. Withthe movement above, the molten metal 50 in the hollow portion 60 isinjected into and filled in the cavity 75 (not shown) in the metal mold70 via the sprue sleeve 71, the mold sprue 72, the runner 73, and thegate 74 (not shown).

In the injection device 1, the cooling medium M1 flows in the firstcooling chamber 121 so as to cool the molten metal 50 accumulated in thehollow portion 60 to such an extent that the molten metal 50 is notsolidified, thereby cooling of the injected molten metal 50 filled inthe cavity of the metal mold 70 can be promoted. Further, after that,detachability between the plunger tip 12 and a biscuit produced bysolidifying the molten metal 50 can be improved.

After the product is produced using the metal mold 70, the processesdescribed in FIGS. 3 to 7 are repeated.

As described above, the injection device 1 according to the firstembodiment further includes, inside the plunger tip 12, the secondcooling chamber 122 provided along the outer peripheral surface of theplunger tip 12 in addition to the first cooling chamber 121 forpromoting solidification of the molten metal after being filled into thecavity. Therefore, in the injection device 1, the cooling medium M2 iscaused to flow in the second cooling chamber 122 before causing thecooling medium M1 to flow in the first cooling chamber 121 such that themolten metal in proximity to the entrance of the gap between the outerperipheral surface of the tip end of the plunger tip 12 and the plungersleeve 11 is solidified before the molten metal enters the gap. Withthis configuration, in the injection device 1, creation of burrs betweenthe outer peripheral surface of the tip end of the plunger tip 12 andthe plunger sleeve 11 can be suppressed, which enables smooth sliding ofthe plunger tip 12. Accordingly, the injection performance can beimproved.

In the first embodiment, the case where the second cooling chamber 122is configured independently of the first cooling chamber 121 and isconfigured such that the cooling medium M2 different from the coolingmedium M1 flowing in the first cooling chamber 121 flows in the secondcooling chamber 122 is described. However, the disclosure is not limitedto this. For example, even when the second cooling chamber 122 is notindependent of the first cooling chamber 121, the second cooling chamber122 may only be provided along the outer periphery of the tip end insidethe main body of plunger tip such that the cooling medium flows in thesecond cooling chamber 122 in priority to the first cooling chamber 121(for example, at an earlier timing).

Second Embodiment

FIG. 8 is a schematic sectional view showing a part of an injectiondevice 2 according to a second embodiment. Compared with the injectiondevice 1, the injection device 2 shown in FIG. 8 further includes astepped shape 123 on the outer peripheral surface of the tip end of theplunger tip 12.

With this configuration, in the injection device 2, the molten metal 50at a stepped portion in proximity to the entrance of the gap between theouter peripheral surface of the tip end of the plunger tip 12 and theplunger sleeve 11 can be solidified quickly before the molten metal 50enters and reaches the depth of the gap.

Structures and operations of the injection device 2 other than the aboveare the same as those of the injection device 1, and thus thedescription thereof is omitted.

Third Embodiment

FIG. 9 is a schematic sectional view showing a part of an injectiondevice 3 according to a third embodiment. In the injection device 3shown in FIG. 9, compared to the injection device 2, the plunger tip 12is further configured to be rotatable about an axial direction (X-axisdirection) as a rotation axis.

In the injection device 3, as the plunger tip 12 is rotated, a hightemperature portion of the plunger tip 12 that is immersed in the moltenmetal 50 is switched with a low temperature portion that is not immersedin the molten metal 50. Therefore, the molten metal 50 in proximity tothe entrance of the gap between the outer peripheral surface of the tipend of the plunger tip 12 and the plunger sleeve 11 can be solidifiedmore quickly using the low temperature portion.

Structures and operations of the injection device 3 other than above arethe same as those of the injection device 2, and thus the descriptionthereof is omitted.

In the third embodiment, the case has been described as an example wherethe plunger tip 12 provided in the injection device 2 is configured tobe rotatable about the axial direction as the rotation axis, but thedisclosure is not limited to this. Needless to say, the plunger tip 12provided in the injection device 1 may be configured to be rotatableabout the axial direction as the rotation axis.

In the first to third embodiments, the case where both the cooling mediaM1, M2 are coolant has been described as an example, but the disclosureis not limited to this. The cooling media M1, M2 may be, for example,liquid nitrogen. With this configuration, the molten metal 50 inproximity to the entrance of the gap between the outer peripheralsurface of the tip end of the plunger tip 12 and the plunger sleeve 11can be solidified more quickly. Further, the cooling media M1, M2 may bedifferent types of cooling media from each other.

What is claimed is:
 1. A plunger tip, comprising a main body of theplunger tip, wherein: a first cooling chamber is provided at a centralregion of a tip end of the main body of the plunger tip inside the mainbody of the plunger tip; and a second cooling chamber is provided insidethe main body of the plunger tip along an outer peripheral surface ofthe tip end, the second cooling chamber being configured such that acooling medium flows in the second cooling chamber in priority to thefirst cooling chamber.
 2. The plunger tip according to claim 1, whereinthe second cooling chamber is configured such that the cooling mediumflows at a timing earlier than a timing of the first cooling chamber. 3.The plunger tip according to claim 1, wherein the second cooling chamberis configured independently of the first cooling chamber and configuredsuch that the cooling medium different from a cooling medium flowing inthe first cooling chamber flows in the second cooling chamber.
 4. Theplunger tip according to claim 3, wherein the cooling medium to flow inthe second cooling chamber of the plunger tip is liquid nitrogen.
 5. Theplunger tip according to claim 1, wherein the outer peripheral surfaceof the tip end of the plunger tip includes a stepped shape.
 6. Aninjection device, comprising: a plunger sleeve having a cylindricalshape; the plunger tip according to claim 1, the plunger tip beingconfigured so as to be slidable in a cylinder of the plunger sleeve; anda plunger rod that causes the plunger tip to slide in the cylinder ofthe plunger sleeve.
 7. The injection device according to claim 6,wherein the plunger tip is configured so as to be rotatable about anaxial direction as a rotation axis.
 8. An injection method of aninjection device including a plunger sleeve having a cylindrical shape,a plunger tip configured to be slidable in a cylinder of the plungersleeve and including a main body of the plunger tip, and a plunger rodcausing the plunger tip to slide in the cylinder of the plunger sleeve,wherein a first cooling chamber being provided in a central region of atip end of the main body of the plunger tip and a second cooling chamberbeing provided along an outer peripheral surface of the tip end insidethe main body of the plunger tip, the injection method comprising:causing a cooling medium to flow in the second cooling chamber inpriority to the first cooling chamber; supplying molten metal into thecylinder of the plunger sleeve; and injecting the molten metal bycausing the plunger tip to slide using the plunger rod while the coolingmedium is caused to flow in the first cooling chamber.
 9. The injectionmethod according to claim 8, wherein the cooling medium is caused toflow in the second cooling chamber before the molten metal is suppliedinto the cylinder of the plunger sleeve.